The social-media giant on Tuesday said it removed 32 pages and accounts from its main service and Instagram photo-sharing app that were created between March 2017 and May of this year. The pages and accounts—which include such names as “Aztlan Warriors,” “Black Elevation” and “Resisters,” and largely targeted causes on the left.

Facebook executives… acknowledged that they identified them only two weeks ago, about 15 months after the accounts started buying ads.

The revelation shows how Facebook continues to struggle with preventing misuse of its platform despite waves of criticism and the company’s repeated pledges to address the problem.

The disclosure also raises the specter of ongoing interference in U.S. politics just over three months ahead of the midterm elections.